Sunday, 9 September 2007

Do glasses make your eyes worse?

The complaint is fairly common once people start using glasses. Before, if they really strained, they could just make out the writing on the TV. But since using glasses, the TV is a total blur without them. Its almost as if once you start using glasses, you kiss naked eye vision goodbye.

Is there any truth to this?

Sort of, yes. It's actually an optical illusion of sorts, brought about by the way the brain processes visual information.

With poor eyesight, the image on your retina is blurry, despite the best efforts of your eye to sharpen the image. But the brain can do slightly better than this. It takes the blurry retinal image and sharpens it up even further - it's a bit like the "sharpen" feature on photo editing software.

So far so good. But when you wear glasses, the retinal image is suddenly sharpened by means of the clever optician. Since the brain no longer needs to sharpen it further, it shuts this function down. And the result? Your vision actually does appear worse when you take your glasses off again, compared to how it was before you got your glasses.

The effect is entirely reversible though - if you lose your glasses for long enough without replacing them, your vision will improve a bit. But obviously only back to the previous level: you'll still need those glasses.

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